This invention relates generally to a surface measurement apparatus, and more particularly to a reflection electron holography apparatus suitable for the precise measurement of undulation of the surface of a solid specimen and for the measurement of magnetic field perpendicular to a specimen.
According to the prior art, as described for example in Optic Suppl. 3 77 (1987) page 4 and Jpn. J. Appl. Phys. vol. 27 No. 9 (1988/9) pp. L1772-L1774, electron waves reflected from a specimen are caused to interfere with each other in an electron microscope to obtain about ten interference fringes whose shifts are measured to determine the height of a surface step. The phases of reflected waves are modulated by undulation on the surface of a specimen. In the prior art, the interference pattern is produced between object waves (reflected waves from a specimen) and therefore difficult for the analysis thereof, which is quite different from that of an usual interference micrograph where a reference plane wave interferes with an object wave modulated by a specimen. If a reflected wave were made to interfere with a direct wave (a wave not illuminating a specimen), the interval between interference fringes would become narrower than the resolution limit of a presently available electron holography apparatus, necessarily leading to an electron hologram generated by interference between reflected waves as in the prior art.